Illuminating apparatus.



W. DA. RYAN. ILLUMINATING APPARATUS. APPLICATION FILED NOV. I9. 1914.

Patented Mar. 6,

Inventor U P h a. w

WALTER DA. RYAN, OF NORTH ADAMS, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ILLUIVIINATING APPARATUS.

release.

Specification of Letters Patent.

Patented Maiu'fi, 1917.

To all whom it may concern:

Be it known that I, Curran DA. RYAN a subject of the King of Great Britain, residing at North Adams, in the county of Berkshire, State of Massachusetts, have invented certain new and useful Improvements in Illuminating Apparatus, of which the following is a specification.

My invention relates to illuminating apparatus, and more particularly to apparatus for directing or projecting light in a definite and more or less concentrated beam. Among the advantages obtainable .through my invention are the utilization in the beam of practically all the available light and the direction of the light in such a way that for all practical purposes the beam shall be actually luminous throughout its entire apparent crosssection, so that when it falls upon an object or surface there shall be no dark spots or shadows. The invention lends itself especially to the production of a beam of nearly uniform width (such asis usually termed a parallel beam) from a relatively concentrated artificial light -source,such as an electric are or a compactly arranged filament of an incandescent electric lamp,and I have hereinafter referred more particularly to this application. Nevertheless, it will be seen that the invention can advantageously be employed when it is desired to direct light efficiently in a definite beam not so concentrated or uniform in projected area as to be properly termed a parallel beam.

In accordance with my invention, I asso ciate with the light source reflector means which acts to throw the light falling on it therefrom forward in a beam such as it is desired to produce. IVith this reflector means I associate means in front of the light source which acts to transmit and direct forward properlythe light from the source that would otherwise escape divergently in front of the reflector means in such a way as to be practically useless, and also, ordinarily, reflector means behind the source which acts to throw the light therefrom falling on it forward to the means in front of the source in such a way that it will be transmitted thereby so as to be properly incorporated in the beam. For convenience. I will hereinafter arbitrarily distinguish the reflector meansthat initially throws the light forward in the proper manner as thcmain re fiector' means and the other as the auxilifollows, first, that the auxiliary reflector means may in practice be dispensed with when the directing means is so constructed and arranged that only a very small amount of light will fall on the auxiliary reflector means, and second, that although when both the two reflector means are employed they may be structurally united, their action and their surface forms must nevertheless be quite different. v

I have hereinafter illustrated and described the best forms of apparatus for the purposes of my invention at present known to me; but while my invention extends to various special features and details of construction and combinations and arrangements of parts herein set forth, it is not confined thereto, but can be otherwise carried out and embodied. Various advantages obtainable in connection with the invention besides those above mentioned will appear from the description, while the scope of the invention will be indicated in my claims.

In the drawing Figure 1 is a mid-sectional view of a projector apparatus constructed in accordance with my invention, the light source for which it is particularly adapted being a tungsten filament incandescent electric lamp; and Fig. '2 is a somewhat diagrammatic mid-sectional view through a modified form of apparatus, the scale being smaller than in Fig. 1.

The apparatus shown in Fig. 1 comprises a base and standard 1 that can be con-.-

veniently mounted on any desired structure and af hollow fitting 2 secured thereto by a universal ball or other adjustablepivotal joint 3. Through the rear end of the fitting 2 extends a tube at that contains current supply wires, 5, 5, and on thefrontend of the tube 4 is mounted a "lamp socket 6. The tube 4 can be moved backward or forward in its hole in the rear wall of the fitting 2 for fo- 0 in any approved manner in a ring cusing adjustment, and a set-screw 7 serves to secure it in any desired position. The fiarin sheet metal reflector 8 shown has a cylin rical neck 9 that fits and is riveted in the open front end of the fitting 2. The transmitting and directing means in front of the incandescent lamp 10 in the socket 6 is shown as a lens 11 mounted in a skeleton framework 12 that is supported in the reflector 8 by means of,- say, three metal strip members 13 riveted or screwed to the frame work and screwed to the reflector. These members 13 are twisted edge-on to the light, so as to interfere with it as little as possible. T heframe-work 12 is composed of two rings 14, 14, joined by strips 15, 15, etc.: it may be made by punching portions from a single wide strip of sheet metal and bending it to circular form. The lens means 11 is secured 16 (as by ventilated flanges or lugs) which is in turn frictionally secured in the framework 12.

As the projector shown is specially designed to give as nearly a parallel beam as possible, the forward, outer portion 17 of the reflector 8, which serves as the main reflector means, is made with a parabolic refleeting surface, and the incandescent lamp 10 is ordinarily adjusted with the parabolic focus in its filamentary light source 18, as near its center as-may be, so that all the light from the filament 18 falling on the refleeting surface 17 will be thrown directly forward parallel with the axis of the parabolic surface. The lens means 11 shown is a converging lens whose principal focus co- -incides as nearly as possible with that of the main reflector means 17, so that the light received by the lens directly from the filament 18 shall be transmitted and directed parallel with the axis of said reflector means The rearward, central portion 19 of the reflector 8, which serves as the auxiliary reflector means behind thev filamentary light source 18, is made with a spherical reflecting surface having its center of curvature as nearly coincident with the focus of the main reflector means 17 as possible, so that the light reaching it directly from the filament shall be directed back therethrough (or approximately so) to the lens means 11 and be transmitted and directed forward by it parallel withlhe main reflector axis, just as though it reached said lens means directly. As shown, the front reflector portion 17 is screwed to the rear portion 19,

vwhich is integral with the neck 9; this construction facilitates manufacture without impairing accuracy or efliciency to any extent that will be appreciable for most ordinagry purposes.

The lens means 11 should preferably be as small in respect of the area of its Projection parallel with the axis of the main reflector means 17 as is consistent with its receiving release all the light fronr the filamentary source 18 that would otherwise escape in front of the main reflector means 17 this is in order that it may not encroach on the projection of light by said main reflector means either by receiving light direct from the source 18 that would naturally reach said mainreflector means or by interfering with light received and thrown forward by said main reflector means. he met by arranging the lens means 11 as close to the filamentary light source 18 as is practicable (the limiting factors being the temperature of the source and the presence of its envelop or bulb, etc.) and giving it a concave form. As the bulb of the incandercent lamp 10 shown is a spherical one concentric with the filament 18, in order to avoid or minimize reflection by said bulb, the lens means 11 is likewise made spherical on its rear side with a cavity 20 for the bulb tip, the necessary divergent properties being secured by a proper disposition of the lens material Fresnel fashion at the front side. As the spherical auxiliary reflector means 19 is intended to receive and direct to lens means 11 all and only all the light that the parabolic main reflector means would itself direct thereto if sufficiently extended to the rear, it will readily be seen that the size of said auxiliary reflector means 19 as regards the area of its projection parallel with the axis of the main flector means 17 should be about the same as that of the lens means ll.

This requirement can best l have spoken above of the lens means 11 merely as a Fresnel type of lens spherical at its rear side; but from its cross-section as shown in Fig. 1 it will be seen that its outer portion near the ring 16 presents certain special features. In the first place, it will be seen that the active outer surface 21 of the last sharp tooth is less nearly cylindrical than would ordinarily be the case, and

that the portion 22 of the inner surface of ,1.

the lens through which the light reaches saidactive surface 21 differs from the spherical in being turned forward to make up for this peculiarity of the surface 21. ln the second place, it will be observed that none 11 of the light striking the inner surface of the lens 11 behind the portion 22 is properly directed forward by refraction alone, part of it being totally lost as far as the beam is concerned, and the rest being refracted at the surface 23 (which differs from the spherical in being more nearly cylindrical) and internally reflected straight forward at the edge surface 24. The reasons for these peculiarities are the relative inefficiency of refraction at surfaces nearly parallel with the desired final direction of the light and the practical exigencies of mounting and securing the lens. Of course it will be understood sion will be in the from which surfaces are not absolutely accurate in the drawing, owing to the small scale; but those skilled in such matters will have no difiiculty in determining the exact angles and contours for the particular glass used and the conditions of each case. In some instances the refinement'of the special surfaces 21, 22, 23, and 24 may be unnecessary while in others even greater refinements may be advisable. For strictly parallel beam work, it is-desirable that the filamentary light source 18 should approximate a mathematical point as closely as may be. This ideal cannot, how.- ever, be realized; and in practice it will be found best to arrange the filament 18 in such a form and position that its greatest dimendirection of the parabolic axis, since in this way the divergence of the forwardly projected light rays from various portions thereof will be minimized. As shown, the wire forming the filament 18 is wound forward from one of its leads in a single helix and then carried back through the center of the helix to its other lead. The axis of the helix is arranged as nearly as possible coincident with the axis of the re flector means 17.

In Fig. 2 I have shown somewhat diagrammatically a lamp in which only the main reflector means 30 is employed, the filamentary light source 31 being arranged at its parabolic focus and the lens means '32 and bulb 33 being'similar to those.

shown in Fig. 1 but smaller in proportion to the size of the reflector 30. Owing to the closeness of the lens means 32 to the filamentary source 31 which the reduced size of the bulb 33 permits, the lens means is smaller as regards projected area and the amount of light returned to it b the reflector means 30 is correspondingly l be seen, therefore, bility of employing 0r omitting the auxiliary reflector means depends largely on the size of the lamp bul The most eflicient light directing part of both forms of apparatus is the main reflector means, and the least eflicient portion of an lens means is that whose refracting surface most nearly coincides with the direction of the light leaving it. In every case the size and the shape of the lens means should be designed to give the best compromise among the three main controllable factors loss arises: escape of light dive'rgently in front of the main reflector means: inefliciency of even' the best lens means in comparison with the main reflector means; and excessive inefficiency of refracting surfaces nearly coincident with the direction of the light leaving them. Although, therefore, the size of the lamp bulb will often 'be so large that the best lens means will be one conforming to its front portion so as to be of the smallest size that will preess. It will that the practical desirator means more than in the'apparatus of.

Fig. 1, since in the apparatus of Fig. 2 all the light thrown forward to the lens means 32 by the main reflector means 30 is a dead loss so far as the beam is concerned; indeed, unless the lens means 32 is made very decidedly concave it will, ordinarily be so large as to render this form of apparatus practically useless.

. It will be readily seen that in any projector apparatus a certain portion of the light emanating from the source'will not be practically available because cut off by the lamp base or other structural parts or lost in the opening in the reflecting surface where the lamp is mounted, etc., and that either all or only part of the remaining light may be acted on and thrown forward by the reflecting and other directing parts of the apparatus with whatever efliciency they have. In an ordinary well-designed simple parabolic projector with an incandescent lamplight source, the light notacted on and so entirely lost, including that unavailable as above set forth, amounts to about 40% of the total; in the apparatus of Fig. 2, the light lost because not acted on amounts to about 20%, including that necessarily unavailable; in the apparatus of Fig. 1, however, the light lost because not acted on includes only that necessarily unavailable and need not be more than about 8%. In all three cases the actual efliciencies are, of course, somewhat less than these figures would indicate owing to the inevitable in-,

, said reflector means; and auxlliary reflector means behind said source for directing back therethrough to said means'in front thereof the rest "of the available light from the source, said lens means being concave and conforming as closely as possible to the adjacent surface of the envelop and being of the smallest size consistent with its receiving substantially all the light that would otherwise escape in front of said reflector means as aforesaid, and said auxiliary re-- fiector means being of the smallest size conemma the smallest size consistentwith its ing substantially all the light from the lilament that would otherwise escape divergently in front of said reflector, and said spherical reflecting surface being of substantially the same size as said lens means.

In witness whereof, I have hereunto set my hand this thirteenth day of November,

WALTER DAr. RYAN.

Witnesses LoUIs H. Nam, R. L. RADKE. 

